RFR 8147794: Jlink's ModuleEntry.stream can't be consumed more than once and ModuleEntry content should be read only if needed

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8147794/webrev.00/ for
https://bugs.openjdk.java.net/browse/JDK-8147794

Thanks,

-Sundar